This invention relates generally to magnetic bubble memory devices and more particularly to a means for providing the rotating in-plane magnetic field for moving bubbles from one location to another in a field of memory elements.
The presently adopted method of propagating bubble domains in a bubble memory consists of a coil structure surrounding the bubble memory device which is electrically driven to produce the rotational in-plane field. Typically, the coil structure consists of a pair of coils, with one oriented towards an X axes and the other oriented towards a Y axes so that the two coils are fitted together. These coils typically add considerably to the power consumption and volume requirements for a given size bubble memory. The theory of such propagation systems is explained in an article entitled "Propagation of Cylindrical Magnetic Domains in Orthoferrites," by Anthony J. Perneski, IEEE TRANSACTIONS ON MAGNETICS, Volume Mag-5, Number 3, September 1969, pages 554 through 557. FIG. 2 in that article is generally illustrative of the type of coil structure required.
It would be desirable to have a means for generating an in-plane field for propagating magnetic bubbles which does not add significantly to the volume of the structure for a given size memory or add to the power requirement as significantly as the conventional coil structure now used. However, in the field access method of operating a bubble memory, the coil system for producing the rotating field has been the only satisfactory arrangement. It is noted, however, that the prior art also includes an effort at developing a conductor driven bubble propagation scheme. A description of the conductor driven bubble propagation scheme is contained in the article "Magnetic Bubbles" by Andrew H. Bobeck and H. E. D. Scovil, SCIENTIFIC AMERICAN, June 1971, pages 78 to 90. The conductor driven bubble propagation scheme consists of conductor loops placed directly over a magnetic wafer. Unlike the field access system there are no permalloy elements which act to contain or restrain the magnetic bubbles. The conductor loop driven system constrains the magnetic bubble within patterns formed on parallel conducting elements.
Problems with the prior art conducting loops are the extremely precise controls on spacing and shape of the conductors in order to provide a satisfactory memory. The advantage of the field access bubble memory system employing an externally generated rotating field with permalloy elements is that the only material which had to be placed on the magnetic substrate was the pattern of permalloy elements which could be much larger than the desirable bubble size. In contrast, the size and spacing of conductors in a prior art conductor access method required conductors to be of approximately the same size as the bubbles to be propagated.